Intraoperative Neurophysiological Monitoring in Tethered Cord Syndrome Surgery: Predictive Values and Clinical Outcome.

INTRODUCTION: "Tethered cord syndrome" (TCS) refers to a congenital abnormality associated with neurological signs and symptoms. The aim of surgery is to prevent or arrest their progression. This study reports a retrospective case series of tethered cord syndrome surgeries, supported by intraoperative neurophysiological monitoring. METHODS: The case series comprises 50 surgeries for tethered cord syndrome in which multimodal intraoperative neurophysiological monitoring was performed using motor evoked potentials (transcranial motor evoked potentials [TcMEPs]), tibial nerve somatosensory evoked potentials (TNSEPs), and pudendal-anal reflex (PAR). The intraoperative neurophysiological monitoring results are reported and correlated with clinical outcomes. RESULTS: Sensitivity, specificity, and negative predictive value were high for TcMEPs and TNSEPs, while PAR exhibited low sensitivity and positive predictive value but high specificity and negative predictive value. Fisher's exact test revealed a significant correlation between changes in TcMEPs, TNSEPs, and clinical outcome ( P < 0.000 and P = 0.049 respectively), but no correlation was detected between PAR and urinary/anal function ( P = 0.497). CONCLUSIONS: While TcMEPs and TNSEPs were found to be reliable intraoperative neurophysiological monitoring parameters during tethered cord syndrome surgery, PAR had low sensitivity and positive predictive value probably because the reflex is not directly related to bladder function and because its multisynaptic pathway may be sensitive to anesthetics. New onset muscle weakness and sensory deficits were related to postoperative changes in TcMEPs and TNSEPs, whereas changes in PAR did not predict bladder/urinary impairment. Urinary deficits may be predicted and prevented with other neurophysiological techniques, such as the bladder-anal reflex.

Intraoperative ECoG in bottom-of-the-sulcus syndrome using a novel flexible strip electrode.

The recording of epileptiform discharges from bottom-of-sulcus focal cortical dysplasia (BOSD) is often difficult during intraoperative electrocorticography (ECoG) due to the deep localization. We describe the use in this scenario of a new-generation electrode strip with high flexibility, easily adapted to cortical gyri and sulci. A right-handed 20-year-old male with drug-resistant focal epilepsy due to BOSD of the inferior frontal gyrus and daily focal aware seizures was evaluated for epilepsy surgery. Based on electroclinical and neuroimaging results, a focal cortectomy guided by ECoG was proposed. ECoG recordings were performed with new-generation cortical strips (Wise Cortical Strip; WCS®) and standard cortical strips. ECoG, performed on the convexity of the frontal cortical surface, recorded only sporadic spikes with both types of strips. Then, after microsurgical trans-sulcal dissection, WCS was molded along the sulcal surface of the suspected BOSD based on 3D-imaging reconstruction, showing continuous/subcontinuous 3-4-Hz rhythmic spike activity from the deepest electrode. Registration after resection of the BOSD did not show any epileptiform activity. Pathology showed dysmorphic neurons and gliosis. No surgical complications occurred. The patient is seizure-free after 12 months. This single case experience shows that highly flexible electrode strips with adaptability to cortical gyrations can identify IEDs originating from deep location and could therefore be useful in cases of bottom of the sulcus dysplasia.

Surgery for intramedullary spinal cord ependymomas in the neuromonitoring era: results from a consecutive series of 100 patients.

OBJECTIVE: The established treatment of intramedullary spinal cord ependymomas (ISCEs) is resection. Surgical series reporting treatment results often lack homogeneity, as these are collected over long time spans and their analysis is plagued by surgical learning curves and inconsistent use of intraoperative neurophysiological monitoring (IONM). The authors report the oncological and functional long-term outcomes in a modern series of 100 consecutive ISCEs that were resected between 2000 and 2015 by a surgically experienced team that consistently utilized IONM. METHODS: In this retrospective study, the authors tailored surgical strategy and multimodal IONM, including somatosensory evoked potentials, muscle motor evoked potentials (mMEPs), and D-waves, with the aim of gross-total resection (GTR). Preservation of the D-wave was the primary objective, and preservation of mMEPs was the second functional objective. Functional status was evaluated using the modified McCormick Scale (MMS) preoperatively, postoperatively, and at follow-up. RESULTS: Preoperatively, 89 patients were functionally independent (MMS grade I or II). A GTR was achieved in 89 patients, 10 patients had a stable residual, and 1 patient underwent reoperation for tumor progression. At a mean follow-up of 65.4 months, 82 patients were functionally independent, and 11 lost their functional independence after surgery (MMS grades III-V). Muscle MEP loss predicted short-term postoperative worsening (p < 0.0001) only, while the strongest predictors of a good functional long-term outcome were lower preoperative MMS grades (p < 0.0001) and D-wave preservation. D-wave monitorability was 67%; it was higher with lower preoperative MMS grades and predicted a better recovery (p = 0.01). CONCLUSIONS: In this large series of ISCEs, a high rate of GTR and long-term favorable functional outcome were achieved. Short- and long-term functional outcomes were best reflected by mMEPs and D-wave monitoring, respectively.

Long-term motor deficit in brain tumour surgery with preserved intra-operative motor-evoked potentials.

Muscle motor-evoked potentials are commonly monitored during brain tumour surgery in motor areas, as these are assumed to reflect the integrity of descending motor pathways, including the corticospinal tract. However, while the loss of muscle motor-evoked potentials at the end of surgery is associated with long-term motor deficits (muscle motor-evoked potential-related deficits), there is increasing evidence that motor deficit can occur despite no change in muscle motor-evoked potentials (muscle motor-evoked potential-unrelated deficits), particularly after surgery of non-primary regions involved in motor control. In this study, we aimed to investigate the incidence of muscle motor-evoked potential-unrelated deficits and to identify the associated brain regions. We retrospectively reviewed 125 consecutive patients who underwent surgery for peri-Rolandic lesions using intra-operative neurophysiological monitoring. Intraoperative changes in muscle motor-evoked potentials were correlated with motor outcome, assessed by the Medical Research Council scale. We performed voxel-lesion-symptom mapping to identify which resected regions were associated with short- and long-term muscle motor-evoked potential-associated motor deficits. Muscle motor-evoked potentials reductions significantly predicted long-term motor deficits. However, in more than half of the patients who experienced long-term deficits (12/22 patients), no muscle motor-evoked potential reduction was reported during surgery. Lesion analysis showed that muscle motor-evoked potential-related long-term motor deficits were associated with direct or ischaemic damage to the corticospinal tract, whereas muscle motor-evoked potential-unrelated deficits occurred when supplementary motor areas were resected in conjunction with dorsal premotor regions and the anterior cingulate. Our results indicate that long-term motor deficits unrelated to the corticospinal tract can occur more often than currently reported. As these deficits cannot be predicted by muscle motor-evoked potentials, a combination of awake and/or novel asleep techniques other than muscle motor-evoked potentials monitoring should be implemented.

Intraoperative neurophysiological monitoring in aneurysm clipping: Does it make a difference? A systematic review and meta-analysis.

The use of intraoperative neurophysiological monitoring (IOM) has been proposed to prevent new neurological deficit during aneurysm clipping. The purpose of this meta-analysis was to evaluate if IOM can prevent neurological injury during clipping of intracranial aneurysm. Using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines for systematic reviews and meta-analysis, we reviewed clinical comparative studies who evaluate the rate of new neurological deficit in patients who had a surgical clipping with and without IOM. Of the 268 citations screened, four studies (including 873 patients) met the inclusion criteria and were included in the meta-analysis. Patients who received surgery with IOM had less new neurological deficit than those who underwent surgery without it (p = 0,04). This finding was more significant in the subgroup analysis of two studies focused on middle cerebral artery (MCA) aneurysm (p = 0,02). However, a specific analysis of the three studies reporting the results of IOM to prevent permanent deficit revealed that there is only a trend for less neurological events in monitored patients without statistically significance (p = 0,05). The use of IOM during clipping of intracranial aneurysm was associated with less new neurological deficit with the obtained evidence of the included studies. However, at long-term follow-up the use of IOM did not correlate with a significant improvement in neurological outcome.

Cortico-cortical connectivity between the superior and inferior parietal lobules and the motor cortex assessed by intraoperative dual cortical stimulation.

BACKGROUND: The function of the primate's posterior parietal cortex (PPC) in sensorimotor transformations is well-established, though in humans its complexity is still challenging. Well-established models indicate that the posterior parietal cortex influences motor output indirectly, by means of connections to the premotor cortex, which in turn is directly connected to the motor cortex. OBJECTIVE: The possibility that the PPC could be at the origin of direct afferents to M1 has been suggested in humans but has never been confirmed directly. We aim to do so in the present study by using the novel technique of paired intraoperative cortical stimulation. METHODS: In the present cross-sectional study, we assessed during intraoperative monitoring of the corticospinal tract in brain tumour patients the existence of short-latency effects of parietal stimulation on corticospinal excitability to the upper limb. MEPs were evoked by test stimuli over the motor cortex, which were preceded in some trials by conditioning stimuli on the PPC. RESULTS: We identified two active cortical loci. One in the inferior parietal lobule exerted short-latency excitatory effects and one in the superior parietal lobule that drove short-latency inhibitory effects on cortical motor output. All active foci were distributed in the rostral portion of the PPC and on the postcentral sulcus. CONCLUSIONS: For the first time in humans, the present data show direct evidence in favour of a distributed system of connections from the posterior parietal cortex to the ipsilateral primary motor cortex. In addition, we show that dual cortical stimulation is a novel and efficient technique to investigate intraoperative brain connectivity in the anaesthetized patient.

Intra-operative neurophysiological mapping and monitoring during brain tumour surgery in children: an update.

INTRODUCTION: Over the past decade, the reluctance to operate in eloquent brain areas has been reconsidered in the light of the advent of new peri-operative functional neuroimaging techniques and new evidence from neuro-oncology. To maximise tumour resection while minimising morbidity should be the goal of brain surgery in children as much as it is in adults, and preservation of brain functions is critical in the light of the increased survival and the expectations in terms of quality of life. DISCUSSION: Intra-operative neurophysiology is the gold standard to localise and preserve brain functions during surgery and is increasingly used in paediatric neurosurgery. Yet, the developing nervous system has peculiar characteristics in terms of anatomical and physiological maturation, and some technical aspects need to be tailored for its use in children, especially in infants. This paper will review the most recent advances in the field of intra-operative neurophysiology (ION) techniques during brain surgery, focussing on those aspects that are relevant to the paediatric neurosurgery practice.

Neurophysiology of complex spinal cord untethering.

Surgery of complex spinal dysraphisms can be challenging. A number of surgical maneuvers can place the conus and the cauda equina at risk for neurological injury during cord untethering, and the identification of functional neural structures within the lumbosacral region is often not possible solely on the basis of anatomy. Therefore, the assistance of intraoperative neurophysiological monitoring can be invaluable during these procedures. We describe the intraoperative neurophysiological monitoring strategy developed at our institution over the past 12 years when dealing with tethered cord surgery. Monitoring and mapping techniques are described, with a focus on the invaluable role played by neurophysiological mapping. This latter, for a neurosurgeon, impacts tethered cord surgery at least as strongly as neurophysiological monitoring. Our results suggest that the combination of monitoring and mapping techniques increases the safety of these procedures, minimizing long-term morbidity and improving the degree of cord untethering.

Retained medullary cord confirmed by intraoperative neurophysiological mapping.

INTRODUCTION: A retained medullary cord (RMC) is a rare dysraphic malformation, recently described as a late arrest of secondary neurulation. RMC is also a severely tethering lesion. The critical role of intraoperative neurophysiology to safely manage a RMC has been only anecdotally reported. CASE REPORT: We describe the case of a RMC in a 1.5-year-old child with Currarino syndrome. At surgery, an apparently normal-looking spinal cord, stretched and tethered by a lipoma to the level of S2-S3, was observed. The border between the functional conus and the non functional RMC was defined through neurophysiological mapping. The cord was sharply interrupted at this level and untethered. A specimen was sent for pathology, which confirmed the presence of glial and neural elements. The post-operative neurological exam was normal. CONCLUSION: Neurosurgical procedure for RMC should only be rendered with intraoperative neurophysiological mapping, as the anatomical judgment would not suffice to allow a safe cutting of these "normal-looking" neural structures.

Intraoperative neurophysiology in tethered cord surgery: techniques and results.

INTRODUCTION: Intraoperative neurophysiologic monitoring (IOM) is nowadays extensively used to minimize neurological morbidity in tethered cord surgery. Our goal is to describe and discuss the standard IOM techniques used during these surgical procedures and to summarize our clinical experience using a multimodal IOM approach. MATERIAL AND METHODS: Neurophysiological mapping of the conus-cauda is performed through direct stimulation of these structures and bilateral recording from segmental target muscles. While mapping identifies ambiguous neural structures, their functional integrity during surgery can be assessed by monitoring techniques only, such as somatosensory evoked potentials (SEPs), transcranial motor-evoked potentials (MEPs) from the limb muscles and anal sphincters, and the bulbocavernosus reflex (BCR). RESULTS: Between 2002 and 2012, we performed 48 surgical procedures in 47 patients with a tethered cord secondary to a variety of spinal dysraphisms. The monitorability rate was 84 % for SEPs, 97 % for limb muscle MEPs, 74 % for the anal sphincter MEPs, and 59 % for the BCR. In all patients but one, SEP, MEP, and BCR remained stable during surgery. Postoperatively, two out of 47 patients presented a significant-though transient-neurological worsening. In six patients, an unexpected muscle response was evoked by stimulating tissue macroscopically considered as not functional. CONCLUSIONS: Mapping techniques allow identifying and sparing functional neural tissue and vice versa to cut nonfunctional structures that may contribute to cord tethering. Monitoring techniques, MEP and BCR in particular, improve the reliability of intraoperative neurophysiology, though these may require a higher degree of neuromonitoring expertise. IOM minimizes neurological morbidity in tethered cord surgery.

Intraoperative cortical mapping of visuospatial functions in parietal low-grade tumors: changing perspectives of neurophysiological mapping.

OBJECT: The aim of this study was to explore the feasibility of intraoperative visuospatial mapping with the same criteria currently used to define essential language areas. METHODS: The authors compared surgical procedures in 2 patients with similar tumors (Grade II oligodendroglioma in the right parietal lobe) undergoing awake, image-assisted surgery for lesion removal with intraoperative neurophysiological monitoring. The line bisection task was used in both patients but with different criteria. RESULTS: In the first case, the authors respected any area, even within the tumor, where significant interference was found (a stimulation-induced error in 2 of 3 applications defined an essential area). In the second case, they removed 1 essential area located in the tumor and recorded an uneventful clinical response soon thereafter. They continued to monitor the patient without stimulation and stopped the resection when the patient was close to the criteria valid for defining spatial neglect. The signs of spatial neglect were present for 3 days postoperatively and then cleared spontaneously. Subtotal tumor removal was achieved in both cases. CONCLUSIONS: Evidence in the present study reveals that areas for visuospatial functions cannot be assessed with the same criteria used for language functions, since essential areas located in the tumor can be safely removed.

Frequency and time-frequency analysis of intraoperative ECoG during awake brain stimulation.

Electrocortical stimulation remains the standard for functional brain mapping of eloquent areas to prevent postoperative functional deficits. The aim of this study was to investigate whether the short-train technique (monopolar stimulation) and Penfield's technique (bipolar stimulation) would induce different effects on brain oscillatory activity in awake patients, as quantified by electrocorticography (ECoG). The study population was seven patients undergoing brain tumor surgery. Intraoperative bipolar and monopolar electrical stimulation for cortical mapping was performed during awake surgery. ECoG was recorded using 1 × 8 electrode strip. Spectral estimation was calculated using a parametric approach based on an autoregressive model. Wavelet-based time-frequency analysis was then applied to evaluate the temporal evolution of brain oscillatory activity. Both monopolar and bipolar stimulation produced an increment in delta and a decrease in beta powers for the motor and the sensory channels. These phenomena lasted about 4 s. Comparison between monopolar and bipolar stimulation showed no significant difference in brain activity. Given the importance of quantitative signal analysis for evaluating response accuracy, ECoG recording during electrical stimulation is necessary to characterize the dynamic processes underlying changes in cortical responses in vivo. This study is a preliminary approach to the quantitative analysis of post-stimulation ECoG signals.

Intraoperative neurophysiological monitoring during surgery for Chiari malformations.

Reports on the use of intraoperative neurophysiological monitoring (INM) techniques during surgery for Chiari malformations are anecdotal. There are almost no data on significant intraoperative worsening in either somatosensory-evoked potentials (SEPs) or brainstem auditory-evoked potentials (BAEPs) during surgery that would have alerted the surgeon to modify the surgical strategy. Yet, a few reports suggest that INM may play a role in preventing spinal cord injury during positioning of the patient. Overall, the use of INM in this type of surgery can be considered only as an option. More speculatively, INM adds information to the ongoing discussion on the most appropriate surgical technique for posterior fossa decompression in Chiari malformations. This debate applies especially to children where a more conservative approach is advisable to reduce the complications. Studies on the conduction time of BAEPs provide some evidence that, from a merely neurophysiological perspective, most of the improvement occurs after bony decompression and removal of the dural band at the level of the atlanto-occipital membrane, not after duraplasty.

Surgical treatment of high-grade gliomas in motor areas. The impact of different supportive technologies: a 171-patient series.

In the last few years much has been published to validate new technology in brain mapping for clinical purposes, but there have been few clinical results. In this report we describe our five-year experience in the surgical management of malignant gliomas around motor areas with an evaluation of the impact of functional magnetic resonance imaging (fMRI) plus navigator and intraoperative neurophysiology (IN). End-points were extent of removal, morbidity, and survival. Variables describing patient and tumor characteristics and treatment modalities were statistically weighted in relation to treatment outcome. Tumor depth (P = 0.01), midline shift ≥1 cm. (P = 0.05), and insular location (P = 0.001) negatively affected extent of removal, whereas IN (P < 0.001) and fMRI plus navigator (P = 0.02) contributed to increasing the rate of total removal (73%, 71% vs. 40%). Postoperative motor impairment was mild and transient in a minority of cases (20%). General complications, as defined by the Glioma Outcome Project, occurred in 23% of cases. IN was the only factor associated with acute postoperative motor deterioration (P < 0.001). IN and age >65 years (P = 0.01) were associated with the occurrence of complications. Overall survival was significantly higher in patients operated with IN or fMRI plus navigator (P < 0.01). Comparing different surgical strategies used in the same period, we observed that supportive technologies in glioma surgery have their primary impact on the quality of resection and survival. IN led to transient motor impairment and some additional complications which did not affect functional outcome.